Feasibility of an Integrated Self Biased Coplanar Isolator With Barium Ferrite Films

Abstract

The development of passive devices using a ferrite is a major focus of current research for electronic applications in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe 12 O 19 or BaM), which has a large resistivity and high permeability at high frequencies are indeed of great interest for microwave device applications. In this work we developed an integrated and self-biased coplanar isolator using BaM sputtered films. BaM films, 1-36 m thick, were deposited under optimized conditions by radio frequency magnetron sputtering on alumina substrates. The films were crystallized using a 800 C thermal annealing. Isolators were then realized using patterning of coplanar waveguides (CPW) with standard lift-off technique. The slots and the central width were 300 m wide and gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film's thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate), the CPW metallic thickness and the polarizing field. As standard design, the CPW were deposited on the top of the magnetic film. At the remanent magnetization (no polarizing field applied), the transmission coefficients then showed a non reciprocal effect, which reached 5.4 dB per cm of line length at 50 GHz for a 26.5 m thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate after a selective etching of the BaM film, we measured that the non reciprocal effect reached higher values for lower BaM thicknesses than for the first design and that the insertion losses also decreased. The interaction between the field lines created by the conductors and the magnetic film was indeed favored in the second case. Finally, we show the tunability of the isolator with the polarizing field.

Microstructural and magnetic properties of thick (≥10μm) magnetron sputtered barium ferrite films

“…Our goal is to check whether the BaM films effectively exhibit the gyromagnetic properties that lead to non-reciprocal wave propagation [18][19][20]. Practically the isolator consists of a CPW patterned on the BaM film.…”

New Nanosized (Gd3+, Sm3+) Co-doped Zinc Ferrite for Telecommunication Applications. Magnetic and Structural Properties.

“…Thus, good control of the theoretical formalism of the role of magnetism and magnetic material properties in telecommunication systems and devices, is a great challenge for the advancement of device design and performance. Nanoferrites have been widely studied and applied in antennas [1]- [4] , circulators [5]- [7], insulators [8]- [10] and inductors [11]- [14].…”

Design of a new coplanar isolator made from YIG film operating in the X-frequency band

“…Isolators, among non-reciprocal components, are useful for applications in RF frequency circuits [1] [2]. The ferrite properties in microwave range are used to create non-reciprocal propagation.…”